Multiplex radio receiver



C. J. H. A. STAAL MULTIPLEX RADIO RECEIVER Nov. 4, 1952 2 SHEETS-SHEET 1 Filed Feb. 18, 1948 J6 A E. ZHHHHH J- f u wimfli l i Ll MWWWW ymml WnWMHH .r

7% 4 vll -l ||||i|| |l|| l M iii. H II vi zFi fl/W/l VVU /V a INVENTOR. 001M165 JOHANMES HENRIGl/SANTOMUSJMAL N 1952 c. J. H. A. STAAL 7 I A MULTIPLEX RADIO RECEIVER Filed Feb. 18, 1948 2 SHEETS-SHEET 2 21 22 Z5 Z4 25 26' Z 7 Z8 RECEMNG E a a 5 a a CHANNELS MPLIHER Q -l8 I v PULSE ammes IN V EN TOR.

' WRNELIY JOHANNES' HHYRIGUSAJVTOJVJUJJIAAZ AGENT.

Patented Nov. 4, 1952 Cornelis Johannes Henricus Antonius Staal, Eindh'oven, Netherlands, .assigno'r to Hartford National Bank and Trust Company, Hartford,

Con-11., as trustee Application February 18, 1948, Serial No. 9,166 In the Netherlands March 5, 1947 ZGlaims.

, 1 The, invention relates to multiplex radio-receivers comprising a plurality of receiving channels lacing periodically operative in the rhythm of the *cycle frequency and successively in the rhythm of the switching frequency and adapted toreceive signal pulses which, by their duration or phase, characterize di do-rent :signals. such devices are .used .for the simultaneous reception of several telephone conversations or other signals such, for example, as Morse-signals, telex signals or the like.

Once in each system cycle the receiving channels become operative for a short time, for example, under the-effect of successive rectangular voltage pulses which 'sometimes are referred to as gating-pulses.

The several receiving channels should be opened periodically and successively .in exact isochronism with the opening of corresponding transmitter channels and in connection there with it :is customary to send out one synchronizing pulse per transmission cycle. In such a system one of the transmission channels is frequently utilised for the transmission of synchronizing pulses of a *dura'tionat leastcorresponding toone switching period, in which event consequently the synchronizing pulses are distinguished from the signal pulses by "a longer -duration and may be separated from the latter in the receiver by means of an integrating network (of. Wireless World June 1-946, page 187 Details of Army WirelessStation No. 1 r

A great disadvantage of known jmultiplezi y t m of thezabovedescri-bed type, wherein the signals are transmitted by "pulse-duration or pulse-phase modulation, is the -socalled crosstalkj i. e. the presence in a particular channel of signals originating from other channels.

The applicant has -stated that, besides many other ways of cross-talk, cross talk takes place from the receiving channel operative just before the reception of "the synchronizing pulses to other channels-and this more particularly inthe "case o'i great modulation depth, i. "e. comparatively long maximum duration "or, phase deviation of the signal pulses.

According-to the, invention, in receivers of the type under consideration this disadvantage is almost completely avoided so that greater modu lation depth is permissible, :by :supplying the receivedpul'ses, after amplitude detection, for the purpose of separating synchronizing and signal pulses, through a difierentiatin'gnetwork to a threshold device from the output circuit of which the synchronizing pulses separated from the signal pulses are taken.

The time-constant of the difieren'tiating network should preferably be smaller than the duration of the synchronizing pulses and larger than the (maximum) duration of the signal pulses.

It may be noted here that in television technique it is known to separate lineand imagesynchronizing signals of different duration by means of a diiierentiating network.

The invention will now beexplained more fully with reference to the accompanying drawings for the case of signals .transmitted by pulse-phase modulation.

Fig. 1 shows the pulses received, after amplitude detection, during slightly more than one period of the cycle frequency with a known system comprising nine transmission channels of which one serves I to transmit synchronizing pulses.

Fig. .2 represents the output voltage of an integrating network utilised, in accordance with the known method, vfor separating synchronizing and signal pulses.

Fig. 3 represents the output voltage of a difierentiating network utilised "for separating synchronizing and signal pulses in accordance with the present invention.

Fig. 4 represents, partly as a block diagram, a ci-rcuit arrangement of a multiplex receiver according to the invention.

In Fig. 1 the pulses obtained after amplitude detection, limitation, etc. in a 9-,ch'ann'e1 multiplex system are represented in atime diagram for a duration corresponding slightly more than one cycle period To 99 ,usec.). .A cycle period is subdivided into 9 equal channel periods T! (11 ,usec;), the first of which is taken up each "time by synchronizing pulses 'l, l represented by hatched areas. In the furthers channel periods occur signal pulses 2, 3 8, 2' etc. which have a constant duration (1.5 p.830.) and which characterize the transmitted signal byatheir phasedeviation with respectto the middle (indicated by a dot-dash line) of a channel period.

The signal pulses .3 and 1 exhibit no phase deviation, the signal pulses 2 and 5 exhibit a negative and the signal pulses 4, 5, 8, 9 and? a positive phase deviation, the phase deviation; of signal pulse 9 being .a maximum;

As is well-known, the synchronizing and'signal pulses may be separated by means of an integrating network and a subsequent threshold device. I i

In Fig.2, Vc represents theoutput voltage set up across the condenser of an integrating net-' work with a time constant of -about -'8 ps'ec'rand Va represents the threshold voltage. Whenever 3 the output voltage Vc crosses the threshold voltage Va in the positive direction, 1. e. at the moments ts and ts, a synchronizing pulse occurs in the receiver.

The cause of the cross-talk phenomenon stated by the applicant appears from Fig. 2, for the position of the moment ts or 15's greatly depends upon the time interval between the presence of signal pulse 9 and synchronizing pulses 1'. With maximum positive phase deviation of the signal pulse 9 the condenser voltage Vs (moment ts) crosses the threshold voltage Va appreciably sooner, and this to an extent dependent upon the phase deviation of the signal pulse 9, than with maximum negative phase deviation of this pulse, in which event the condenser voltage would exhibit the variation indicated by a dotted line lil with the moment of crossing (X's which is later than t's by a time interval At. The synchronizing pulses occurring in the receiver thus acquire a phase. modulation which corresponds to the modulation of the signal pulse 9 and which therefore becomes audible in all other channels with the same intensity.

According to the invention, this cross-talk via the synchronization channel is avoided to a high extent by separating the synchronizing and and signal pulses by means of a diflferentiating network.

Fig. 3 represents the voltage Vi set up across the output resistance of a differentiating network as a function of time in the case of an input voltage variation as shown in Fig. 1.

A more advantageous time constant of the differentiating network can now be taken (in the present case about 4 #860.) and, moreover, the considerably steeper flanks of the output voltage counteract variation of the moment at which this voltage crosses the threshold voltage V9. (which is now taken negative) in the negative direction. The phase modulation of the synchronizing pulses occurring in the receiver which remains behind due to the modulation of the signal pulse 9 is so slight that it cannot be represented in the drawing. By taking the measure according to the invention cross-talk via the synchronization channel is thus, in comparison with the known system, considerably reduced without additional costs.

Fig. 4 represents, as far as is necessary in detail, the circuit-arrangement of a multiplex receiver according to the invention. The receiver exhibits 8 receiving channels II to I8 with separate output terminals 2| to 28, which channels become operative, by means of gating pulses fed thereto by conductors 3| to 38, periodically in the rhythm of the cycle frequency and successively in the rhythm of the switching frequency.

The gating pulses are produced by means of pulse generators Al to 48 the number of which corresponds to that of the channels. These genera-tors excite one another in sequence and thus produce a series of successive gating pulses each time after the pulse generator 4| has been excited by a synchronizing pulse.

These synchronizing pulses are taken from a circuit as shown in detail in the lower part of Fig. 4. The radio-signals captured by an antenna 49 and modulated by the pulses shown in Fig. 1 are supplied, after amplification and amplitude detection (50), through a coupling condenser 5! to an amplifier comprising a second- 4 (cathode resistance 53 and parallel condenser 54) and to the presence of a resistance 55 serving to limit the control-grid current on the other hand.

From an output resistance 56 included in the auxiliary cathode lead of the tube 52 are taken amplified pulses of positive polarity which have been given the correct shape; these pulses are supplied, through a coupling condenser 51 and an amplifier 58, in parallel-connection to all the receiving channels H to [8. From an anode resistance 59 of the secondary-emission tube 52 are likewise taken the amplified pulses of negative polarity and correct shape, the polarity of these pulses being now, however, negative and therefore opposite to that shown in Fig. 1. For the purpose of separating synchronizing and signal pulses these pulse signals, which otherwise correspond to those shown in Fig. 1, are supplied to a differentiating network consisting of the series-connection of a condenser 50 and a resistance 6|. The voltage across the resistance 6|, which exhibits the same variation, as shown in Fig. 3, but with opposite polarity, is fed to the control grid of a pen-tode-amplifier 62. Owing to the presence of a cathode resistance 63 and a condenser 64 connected in parallel thereto, the control grid of this tube has a negative grid bias which normally cuts oif the tube of a value such that the tube is made operative only by voltages exceeding the threshold voltage (Va) shown in Fig. 3, which results in that each time the tubes respond only at the end of a synchronizing pulse and then, at the moments indicated in Fig. 3 by ts and #5, a synchronizing pulse of negative polarity is supplied through a coupling condenser 65 to the first of the pulse generators GI to 48, which pulse initiates the successive operation of the receiving channels II to 18.

It is evident that the invention may also be successfully applied if the receiving channels are successively made operative in a manner other than that described above, for example by means of mechanical or electronic distribution switches or the like of any type known per se.

What I claim is:

1 In a multiplex receiver for the reception of perlodically transmitted trains of high-frequency pulses, each train being constituted by a synchronizing pulse of fixed duration and a series of channel pulses, the duration or phase of each channel pulse being modulated in accordance with a distinct intelligence signal, the fixed du- 'ary-emission tube 52 which acts, moreover, as

ration of said synchronizing pulse exceeding the maximum duration of any one of said channel pulses, the combination comprising means to detect the train of high-frequency pulses to pro duce a corresponding train of direct-current pulses, a differentiating network coupled to the output of said detecting means to derive impulses whose time position corresponds to the trailing edge of said direct-current pulses, said network having a time constant at which the amplitude of the impulse corresponding to the synchronizing pulse exceeds the a-mpltiude of the remaining impulses, and a threshold device coupled to the output of said network, said device having a threshold level at which said device is responsive solely to the impulse corresponding to said synchronizing pulse whereby a synchronizing impulse is produced, a plurality of receiving channels, gating means to successively actuate said receiving channels, means to apply said synchronizing impulse to said gating means to control same, and means to apply said directcurrent pulses to said receiving channels.

2. In a multiplex receiver for the reception of periodically transmitted trains of high-frequency pulses, each train being constituted by a synchronizing pulse of fixed duration and constant amplitude and a series of channel pulses of constant duration, the phase of each channel pulse being modulated in accordance with a distinct intelligence signal, the fixed duration of said synchronizing pulses exceeding the fixed duration of said channel pulses, the combination comprising a detector to demodulate the train of highfrequency pulses to produce a corresponding train of direct-current pulses, a. limiter coupled to the output of said detector to limit the amplitude of said direct-current pulses to a predetermined value, a difierentiating network coupled to the output of said limiter to derive impulses therefrom whose time position corresponds to the trailing edges of said direct current pulses, said differentiating network having a time constant which is smaller than the duration of said synchronizing pulse and larger than the duration of said channel pulses, a threshold device 25 Number coupled to the output of said network, said device having a threshold level at which said device responds solely to the impulse corresponding to said synchronizing impulse to produce a p 6 synchronizing impulse, a plurality of receiving channels, gating means to actuate successively said channels, means to impose said synchronizing impulse on said gating means to control same, and means to apply said direct-current pulses from said detector to said receiving channel-s.

CORNELIS JOHANNES HENRICUS ANTONIUS STAAL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,218,067 Faudell Oct. 15, 1940 2,265,979 Below Dec. 16, 1941 2,292,148 Moe Aug. 4, 1942 2,416,330 Labin Feb. 25, 1947 2,418,127 Labin Apr. 1, 1947 2,425,491 Schlesinger Aug. 12, 1947 2,447,233 Chatterjea et al. Aug. 17, 1948 FOREIGN PATENTS Country Date 108,926 Australia Nov. 9, 1939 365,519 Italy Dec. 6, 1938 845,380 France Aug. 21, 1939 

